The present invention relates to a magnetic recording medium which is capable of recording/reproducing information magnetically and a magnetic head apparatus for recording/reproduction and, more specifically, relates to a magnetic recording medium on which track information as one kind of auxiliary information is recorded and a magnetic head apparatus.
On a magnetic disk, at first auxiliary information is written. The auxiliary information is information, which is necessary for recording/reproducing information on/from a magnetic disk, such as track information for locating on a track of a magnetic head, address information for managing a recording position of information, PLL clock information for reading out an address, and the like. A servo writer is known as an apparatus for writing such auxiliary information on a magnetic disk.
In the servo writer, a guide pin which received an instruction from a locating control circuit pushes out a magnetic head so as to determine a position on the disk, and the magnetic head so as to determine a position on the disk, and the magnetic head records auxiliary information given from an auxiliary data preparation circuit. Such servo writer has problems such that a long time is required for writing track information on a magnetic disk, the servo writer is expensive, and the whole of a servo writer apparatus must be installed in a clean room environment.
In order to solve these problems, there is suggested a magnetic disk to which a technique of an optical disk is applied (NIKKEI ELECTRONICS Jul. 19, 1993 (No. 586) p. p. 169-181). The magnetic disk magnetically reproduces a pit formed on the disk surface so as to obtain auxiliary information. The magnetic disk is formed so that a substrate having spiral or coaxially circular grooves is coated with a magnetic film, and pits corresponding to auxiliary information are previously formed on tracks of the substrate. When the auxiliary information is recorded, the magnetic head is moved in a radial direction in an area where the pits are formed, and applies a strong magnetic field so that convex portions and concave portions are magnetized in an identical direction. Next, while the magnetic head is being moved in the same direction in the same area, the magnetic head applies a weak magnetic field having a direction opposite to that of the strong magnetic field so that only the magnetization of the convex portions is inverted. Since the concave and convex areas on the tracks are magnetized respectively in opposite directions, the auxiliary information which was recorded by the pits can be read out by magnetically reproducing it from the tracks. The grooves are formed in order to prevent fracturing of the reproducing signal due to a leakage of magnetic field between tracks.
When the pits are formed on the magnetic disk according to the track information and the magnetization is executed as mentioned above, the auxiliary information can be easily recorded on the magnetic disk, and thus the servo writer is not required. However, since the pit groups formed according to the auxiliary information are formed with intervals on the tracks, an error in reading a tracking error signal becomes great when a disk rotational number is increased or a track pitch is short.
The present invention is achieved with such points in view, and its one object is to provide a magnetic recording medium, in which magnetization changes areas where magnetic flux is changed along the length of tracks are provided so that track information can be recorded easily, and even if a track pitch is narrow, an error in reading the track information does not occur. Moreover, its object is to provide a magnetic recording medium in which groove sections with a non-uniform width along the length of tracks are provided respectively on both sides of the track so that track information can be recorded easily, and an error in reading track information does not occur.
In addition it is another object of the invention to provide a magnetic head apparatus for controlling tracking of a magnetic recording medium using magnetization change areas whose magnetic flux changes, and further to provide a magnetic head apparatus for controlling tracking of a magnetic recording medium having grooves with identical widths.
A magnetic recording medium of the invention is characterized by including: tracks formed on the magnetic layer, along which information is recorded magnetically; and magnetization change areas for tracking control formed on the magnetic layer, from which a change in magnetic flux along the length of the tracks can be read out.
Since the magnetization change areas where the magnetic flux changes along the length of the tracks are provided, the change in magnetic flux is obtained from the magnetization change areas on both sides of the tracks, and these outputs are differentially detected so that the tracking control can be executed. Therefore, track information can be recorded easily on a magnetic disk and can be reproduced accurately.
In addition, a magnetic recording medium of the invention is characterized by including: tracks formed on the magnetic layer, along which information is recorded magnetically; and groove sections for tracking control formed on the magnetic layer, each of said groove sections having a width non-uniform along the length of the tracks and being magnetization change area which is magnetized in a direction opposite to a magnetization direction of the tracks.
Since each of the groove sections has a width non-uniform in the direction along the tracks, when the groove sections are provided on both sides of the tracks, the magnetic flux changes on both sides of the tracks. The changes in magnetic flux on both groove sections are obtained as track information and the changes are subtracted so that the tracking control can be executed. As a result, the track information can be recorded on the magnetic disk easily and reproduced accurately.
Further, the magnetic recording medium of the invention is characterized in that the magnetization change areas are non-magnetic areas whose width is non-uniform along the length of the tracks.
Therefore, the changes in magnetic flux on both the sides of the magnetic areas (tracks) between the non-magnetic areas are obtained as the track information, and the changes are subtracted so that the tracking control can be executed. Accordingly, the track information can be recorded on the magnetic disk easily and reproduced accurately.
Furthermore, the magnetic recording medium of the invention is characterized in that the magnetization change areas which are adjacent to each other have respective widths where change rates are different from each other.
Therefore, since the change rates of the widths of the groove sections formed on both sides of the track are different from each other, even when the track information of both the groove sections are read out by one magnetic head, for example, the track information of the respective groove sections can be obtained through filters according to frequencies of the change rates. As a result, the tracking control can be executed by differentially detecting the track information. In such a manner, the track information can be recorded easily and reproduced accurately.
A magnetic head apparatus of the present invention is characterized by including: a reproduction head section for detecting the change in magnetic flux; and a differential circuit for obtaining a differential signal between outputs detected by the reproduction head section from the magnetization change areas on both sides of the track.
Therefore, the magnetic flux which changes along the length of the tracks is detected by the reproduction head section, and outputs are obtained from the magnetization change areas on both sides of the tracks, and the tracking control is executed so that the output on one side has a value identical to a value of the output on the other side.
In addition, the magnetic head apparatus of the invention is characterized in that the reproduction head sections are arranged on both sides along the length of the tracks.
Therefore, the tracking control is executed in such a manner that the two reproduction head sections detect the changes in magnetic flux on both sides of the track, and the respective outputs are compared so that they have an identical value.
The magnetic head apparatus of the invention is characterized by further including filter circuits connected to the reproduction head sections for obtaining respective outputs corresponding to the adjacent magnetization change areas so as to give a differential signal therebetween to the differential circuit.
Since the changes in magnetic flux are different on both sides of the tracks, when the changes are inputted to the filter circuits according to frequencies of the respective changes, the outputs detected by the magnetic head apparatus can be divided to the respective sides of the tracks, and the tracking control is executed by the differential circuit.
A magnetic head apparatus of the invention for reproduction-use of a magnetic recording medium in which groove sections are formed on both sides of tracks along which the information is recorded, is characterized by including: a reproduction head section for detecting a change in magnetic flux; displacement elements for displacing the reproduction head section in crossing direction of the tracks; and a differential circuit for obtaining a differential signal between outputs corresponding to two displaced positions of the reproduction head section.
Therefore, by means of the reproduction head section, magnetic output signals of three patterns, which are obtained when the reproduction head section is at the center and are on both sides of the center, are obtained. Since the tracking control is executed so that the output signals which are obtained when the reproduction head section is displaced to both the sides have values identical to each other, the track information can be recorded on the magnetic recording medium easily.
In addition, the magnetic head apparatus of the invention is characterized in that the displacement elements are electrostrictive elements, the differential circuit has a first holding circuit for holding a signal amplitude in a first position of the reproduction head section, a second holding circuit for holding a signal amplitude in a second position, and a comparison circuit for comparing the signal amplitudes of the first and second holding circuits, and the magnetic head apparatus is capable of moving the crossing direction of the tracks in accordance with the compared result.
The signal amplitude, which is obtained when the reproduction head section is displaced to one side, is held by the first holding circuit, and the signal amplitude, which is obtained when the reproduction head section is displaced to the other side, is held by the second holding circuit. These signal amplitudes are compared, and the tracking control is executed so that the signal amplitudes have values identical to each other. As a result, the track information can be recorded on the magnetic recording medium easily.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.